The Mercedes-Benz 280S front side marker bulb uses a P21/5W size, while the rear side marker bulb uses a 12821 or 3893 size. The replacement chart covers 1968 to 1976 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz 280S uses three distinct bulb types across its front and rear side marker positions: the P21/5W, the 3893, and the 12821.
The P21/5W is an ECE-standard dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, fitted with a BAY15d bayonet base. It serves the front side marker position on the 280S for model years 1975-1976.
The 3893 is an ANSI-standard dual-filament bulb with a BAY15d bayonet base, rated at 12V and designated for specialty applications. It covers the front side marker position for model years 1968-1971.
Both the P21/5W and the 3893 share the BAY15d bayonet base type. However, they originate from different standards bodies, ECE and ANSI respectively, and their wattage ratings are not specified as equivalent, which is relevant to fitment considerations.
The 12821 is a Philips-designated miniature wedge bulb of the T10 form factor, using a W2.1x9.5d base and rated at 12V, 5W. It is a single-filament bulb, unlike the P21/5W and 3893.
The rear side marker position for model years 1975-1976 uses the 12821, a wedge-base bulb that is physically and electrically incompatible with the BAY15d bayonet-base bulbs used in other positions and years.
For model years 1968-1971, the 280S uses the 3893 in both the front and rear side marker positions, making the bulb type uniform across both positions during that period.
For model years 1975-1976, the front and rear side marker positions require different bulb types, the P21/5W and the 12821 respectively, meaning the two positions are not interchangeable during those years.
The shift from the BAY15d-based 3893 in the rear side marker to the wedge-base 12821 between the 1971 and 1975 model years reflects a change in socket type, making earlier and later rear bulbs physically non-interchangeable.
The W2.1x9.5d base of the 12821 is the standard wedge base used in T10 miniature bulbs, a format common in low-current indicator and marker applications where a single filament at 5W is sufficient.